The standard rectangular shaped 9 volt "transistor radio" battery is used in a wide variety of products (e.g., portable radios, smoke detectors, cameras). In this battery type, the positive and negative terminals are at one end of the battery. To prevent damage to the product, it is often necessary to prevent the battery terminals from improperly electrically connecting with the electrical contacts of the product in which the battery is installed. The battery terminals themselves are configured to facilitate this, in that one terminal is adapted to be a "male" connector and the other terminal is adapted to be a "female" connector, each also having a different diameter. When the device is electrically connected to the battery via a mating cable connector, proper battery polarization is automatically achieved, because per its description, it has two connectors, each of which "mate", or mechanically cooperate, only with one of the male and female connectors on the battery.
However, because product manufacturer may find it more convenient to install batteries in a product without the use of a mating cable connector, and because it is often easier and less expensive to manufacture a product without a mating cable connector, in many applications it is preferable to make a pressure contact against the terminals of the battery with a spring mechanism of some type, rather than using a mating cable connector. In these applications, protecting the product from reverse polarization when incorrectly installed requires some form of mechanical interference. However, due to variation in the lengths of different brands of batteries and tolerance variations within a brand, there is a need for a reverse polarization protection method that compensates for different battery lengths.